Patch written by R. David Murray.

Patch by Martin Richard.  GH PR #365.

Patch by Richard Walker.

the implementation of the IMPORT_NAME opcode.

Patch by Manuel Kaufmann.

SectionName.  These split class GetCfgSectionNameDialog from
configSectionNameDialog.py, temporarily renamed config_sec.py in 3.7.9a2.
More Query subclasses are planned.

In 3.6, the warning is now called an error, making it harder to ignore.

* tracing in the "u" mode now works
* trace_vdelete() with wrong mode no longer break tracing
* trace_vinfo() now always returns a list of pairs of strings

tkinter.Variable class.  They replace old methods trace_variable, trace,
trace_vdelete and trace_vinfo that use obsolete Tcl commands and might
not work in future versions of Tcl.